This proposal aims to investigate the identity of the mammalian photoreceptors responsible for transmitting light signals to the brain and the mechanisms by which they modulate various non-image forming (NIF) visual functions. Rod and cone photoreceptors are best described for detecting light for image formation. They work in concert with a novel class of intrinsically photosensitive retinal ganglion cells (ipRGCs) to detect all light for NIF functions that affect an array of biological functions and behaviors, including sleep- wake cycles and mood. The roles of the each photoreceptor in multiple NIF pathways have not been studied in depth. Thus, the specific aims are 1) to determine which photoreceptor pathways modulate feeding, drinking, body temperature, and general activity rhythms by using mice deficient in specific photoreceptor signaling pathways, 2) to examine if light detection by rods and cones for NIF functions is conveyed to the brain via ipRGCs exclusively, and 3) to elucidate the molecular machinery within the central pacemaker, the suprachiasmatic nucleus, mediating light-induced phase shift responses. These studies are integral to the comprehensive understanding of the functional relationship between photoreceptors in the eye and the pacemaker clock in the brain to modulate biological rhythms. Temporal organization of physiological and behavioral processes are predominantly mediated by light, thus light influences our mental and physical states. These studies have long term implications in understanding and making strides in alleviating symptoms associated with a broad range of disorders, such as Seasonal Affective Disorder (a seasonal form if depression) and chronic sleep disorders, among others. [unreadable] [unreadable] [unreadable]